ANSWER
[tex]x \ne0[/tex]
EXPLANATION
The given problem is
[tex] \frac{13 {x}^{6} }{ 51 {x}^{4} } [/tex]
This is defined if and only if
[tex]x \ne0[/tex]
Even the given expression can be simplified to obtain:
[tex]\frac{13 {x}^{2} }{ 51} [/tex]
The exclusion is
[tex]x \ne0[/tex]
